Pneumatically operated electrical switching device



June 19, 1951 c. R. WOODLAND 2,557,902

PNEUMATICALLY-OPERATED ELECTRICAL SWITCHING DEVICE Filed Nov. 22, 1948 2Sheets-Sheet 1 IN [/5 N TOR CECIL ROBERT WOODLAND.

A TTOR/VE Y.

June 19, 1951 c. R. WOODLAND 2,557,902

PNEUMATICALLY-QPERATED ELECTRICAL SWITCHING DEVICE Filed Nov. 22, 1948 2Sheets-Sheet 2 IN l/E N TOR.

CECIL ROBERT WOODLAND.

A T TORNE).

Patented June 19, 1951 cmreo STATES PATENT omcr.

Pm'immmr .OPERATEDELECTRICATJ SWITCHING DEVICE Cecil Robert Woodland,Liverpool, England, assignor to Automatic Telephone & Electric CompanyLimited, Liverpool, England, a British company Application Noi e'iiilir22, 1948, serial No. 61,428 In Great Britain December 12, 1 947 6Claims. (01. 200-86) The present inventiofi relates to electricswitchmg" devices suitable for operation by changes in fluid pressureandfinds particularly advantagousapplication to switching devicesoperated pneumatically by vehicles passing over a tread memberlocated inthe road surface, Arrangemerits of this type are already known and arewidely'employed as vehicle detectors for use in vehicle-actuated traii ccontrolsystems. s

Usually in such arrangements the tread mernher which is composed ofrubber or similar re-' silient material-- includes a cavity the volumeof which is varied as the vehicle passes over the detector so as toproduce a momentary increase of pressure which: operates theswitchingdevice. Such vehicle detectors are called uponto meet very stringentoperating conditions since they must be sufliciently robust'to'withstand damageby heavy vehicles passing; at high speed while stillbeing sufli'ciently sensitive to produce correct operationwhentraver'sed by a light vehicle such as a bicycle: Moreover theyrequire careful protection to ensure that; their eflicien'cy shall notbe impaired by extremes of temperature and the effects-of moisture andaccumulations of foreign matter on the road-. The general object of; theinvention is-to produce a switching device which will meet theserequirements more satisfactorily than thosehitherto employed and whichwill be cheap to manufacture; easy to'maintain' and reliable in oeration. 7

Aoeording' to the invention, in an electric switching device'suitablefor operation-by changes i'n'iitiid pressure, a flanged diaphragmsupported onand covering theend' of a circular pipe commuh icatin'g witha control chamber is arranged tobe' moved bodily by increase in thepressure of the'fiuid w'ithinthe chamber to cause it to" e'iiect aswitching operation.

The invention'will be better understood from" thefo'llowingdescription'of one method of carry ing itinto eifect,"r'eferencebeinghad to the accompanying drawings comprising Figs. 1 to 4. Fig; 1 showsaplan view of one form of fluid operated switch according to theinvention, Fig. 2 sho'wsa cross sectional view on the line AA in Fi'gi 1in the direction ofthe arrows, while Fig. 3 is'an'elevation viewed fromthe right of Fig. 1. Fig. iris apla'nv'iew of a pair of switches of thetype'show'n'inFigs; 1-3' mounted within a cont'ainer to provide a unitwhich is particularly suitable for giving unidirectional working in avehicle ac'tuated'traific control system.

Considering'now'FigsI 1, 2and 3, the cylindrical body I of the switchingdevice which is prefer- 2 ably of brass has secured to it the inlet pipeII, which is assumed to be-coupled to a flexible tube extending to acavity in the pneumatic tread member set in the road surface so that thetread cavity is connected with the chamber I2. A filter comprising afine wire mesh disc I3 fitted in a circular frame accommodated in arecess of re chamber serves to prevent the passage into the upperchamber of unwanted particles which might interfere with the properfunctioning of the switch. A ring I4 of electrically insulating materialsuch as phenol fibre board separates the diaphragm support member I5from the body I0. Sealing compound may be applied to the upper and lowersurfaces of the insulating ring I4' to secure an air-tight joint. Themember I5 is provided with a circular projecting portion or pipe l6which is undercut on its outside circumferential surface and looselysupports the diaphragm H which is flanged so as to form a circularinverted shallow dish. The diaphragm which is lightly constructed ispreferably or nickel silver but may be of other material having therequisite properties. It has a thin ring or disk I8 of platinum or othersuitable contact material secured to its upper face and so positioned asto'co-operate with four dome-like contacts such as 21 when the"diaphragm is lifted bodily off its seating. The inside diameter of thediaphragm is a' few thousa-ndths of an inch greater than the greatestoutside diameter of the undercut portion I6 so as to permit freemovement and provide a-slight' air leak as will be described later.

The bridge member I9 of phenol fibre board or like insulating materialis mounted on two pillars 2i! and packing sh-im's 23 and is secured byscrews 2! which are threaded into the body It and carry washers'22.

the body II] by the inclusion of insulating sleeves (not shown) overa'portion of each screw in known manner.

The bridge I9 serves to support four similar afbolt 2s.

The contacts 27 are arranged to be equidistant from the ring I8'andaccording to a preferred adjustment the air'gap of the order of .005"whefri'the'di'aphragm' is'at rest. It will be apparent that the "openconstruction of the'swltch' enables the contacts to be viewed easilyduring The member I5 and the pillars 20 remain electrically insulatedfrom the assembly and adjustment stages, and the airgap, which isdetermined by inserting shims 23 of suitable thickness, can be measuredby inserting a feeler gauge.

When the switch is included in a vehicleactuated trafiic control system,it is sealed against atmosphere by enclosing it in a suitablydimensioned and hermetically sealed metal container. The pipe II, whichprotrudes through a wall of the container, is coupled to a flexible tubewhich extends to the cavity formed within a tread of resilient materialwhich is inserted in the surface of the road and over which vehiclespass. In this manner the air within the container, the tread cavity andthe connecting tubing is isolated from the external atmosphere toprevent the ingress of moisture and other foreign matter into thoseparts of the system.

The cavity within the tread member is compressed upon the passage of avehicle and the pressure of air within it and the tube is increasedrelative to that within the switch container. Thereupon the diaphragm ITis lifted bodily off its seating after the manner of a piston and thering I8 is caused to engage with the contacts 21 so that an electricalpath is extended from one pair of linked contacts to the other pair totransmit a signal to the controller equipment. The diaphragm aided bygravity will subsequently fall back on to its seating when the vehiclepasses clear and the air pressures on both sides of the diaphragm areagain substantially equal. Due to the loose fit of the diaphragm on themember I air is enabled to flow from the cavity beneath the diaphragminto the switch container. Thus if a vehicle were to come to rest on thetread member the diaphragm would be lifted initially but would notremain in the operated position. Even if this should happen othervehicles passing over the pad will produce pulses of increased pressurewhich will cause normal operation of the diaphragm. This will not applyof course if the stationary vehicle closes the tread cavity completelyand the further vehicles pass over the detector on the side remote fromthe equipment of Figs. 1-3.

The volume of the switch container is preferably appreciably greaterthan the volume of the tread cavity, the connecting pipe and the cavityI3 and the leakage round the edge of the diaphragm is such that the backpressure within the container does not equalise the forward pressure inthe tread cavity until the aforesaid electrical path has been closed fora useful period. The leakage effect may be increased if found necessaryby slotting the portion I6 of the diaphragm support member I5. Theslight air leak just mentioned will tend to accentuate the efiect thatwhen a vehicle passes clear of the detector there will be a suckingaction which positively.

restores the diaphragm to its seating.

The mounting of the diaphragm I1 freely on the member I6 provides anelectrical advantage in that it has been found that as the diaphragm islifted and restored it tends to rotate slightly and in consequencediffering positions of the contact ring I8 are continually beingpresented to the contacts 21. This arrangement together with the use oftwo pairs of contacts, appreciably reduces the electrical faultliability of the switch. 7 It will be apparent to those skilled in theart that alternative constructions of the switch might be employed, forexample a single contact member could be mounted centrally upon thebridge I9 and a co-operating contact welded to the dia- 4 phragm towhich a light flexible conductor could be connected. In this case asingle make contact combination is provided and one conductorterminating on the controller equipment would be connected to thecontact member on the bridge and the other conductor connected to theflexible lead.

Reference will now be made to Fig. 4 which is a plan view of twopneumatic switches 30 and 3I mounted within a container 32 which isfinally hermetically sealed from atmosphere to provide a unit suitablefor uni-directional working in a vehicle-actuated trafiic controlsystem. The switches are secured to the container 32 by screws (notshown) passing through the base and the end plates 33 and 34 to fitsnugly and are retained by airtight soldered joints. The inlet pipes II, shown temporarily sealed by rubber caps 46, protrude through holes inplate 33. End plate 34 to which the terminal block housing is securedhas four holes fitted with insulating bushes 35 which provide paths forthe bare conductors connecting appropriate switch soldering tags andterminals. It may be mentioned that all possible air leakage paths inthe container created by the jointing of metal members are sealed by aliberal application of solder. I

The terminal block housing 31, shown with the cover removed, is securedto the end plate 34 by the nuts and bolts 38 and 39 and is divided intotwo compartments 40 and 4| by the terminal strip 42 which is ofinsulating material such. as phenol fibre board. The said stripinterlocks with the housing and carries four terminals 43 which aresecured by the hollow screws 44 threaded into the terminals. Theconductors 36 are each passed through a hollow screw and connect with aterminal at a soldered joint. Each terminal is provided with two screws45 for clamping conductors extending to the controller equipment.Compartment 40 is filled with bitumen before the unit is installed toseal the bushed holes and to act as an electrical insulator and thus thecontainer is completely sealed from atmosphere. The unit may be expectedto have to work under arduous conditions, for example below the surfaceof the road or pavement, and is therefore liberally coated with bitumenon the outside surfaces.

When the unit is being installed, the rubber caps 46 are removed and theappropriate flexible tubes extending from the cavities in the pneu matictreads are securely coupled and sealed to the inlet pipes. Theappropriate insulated conductors terminating at the controller equipmentare stripped of insulation at the ends, passed through holes in theright-hand wall of housing 37 and secured to the relevant terminals 43by screws 45. The whole of the stripped portion of the conductors isarranged to be within the compartment 4| which is then filled withbitumen for electrical insulation purposes before the cover is attachedto the terminal block housing.

I claim:

1. A. pneumatically operated electric switching device comprising, incombination, a vertical tubular element, a diaphragm of a diameterslightly in excess of that of the tubularelement positioned normally torest upon the tubular element, said diaphragm being provided with adownwardly extending flange arranged to sur-,

round the upper portion of the vertical tubular element, a pair ofcontact points supported in fixed position relative to the tubularelement, a

contact member carried by said diaphragm, ter-v 2. The switching deviceclaimed in claim 1,

wherein the contact member comprises a ring of contact materialsupported upon the upper surface of said diaphragm and wherein the pairof contact points fixed in position relative to the tubular member islocated to be engaged by said ring when the diaphragm is moved upwardlyso that a circuit is completed between the said pair of contact points.

3. The switching device claimed in claim 2 comprising, in addition, abridge of insulating material fixed relative to said tubular member andspanning the said diaphragm, said contact points being secured to saidbridge so that the clearance between said contact points and saiddiaphragm in its normal position is readily observable and accessiblefor tests.

4. A pneumatically operated electrical switching device comprising incombination a chamber member having an upwardly extending tubularsection, a substantially circular diaphragm of slightly larger diameterthan that of the tubular section positioned to rest in normal state uponthe upper edge of the tubular section, said diaphragm having adownwardly extending flange surrounding a portion of the tubularsection, a contact member carried upon the upper surface of saiddiaphragm, a pair of contact points supported from the said chambermember in fixed location relative thereto and positioned to be contactedby the contact member carried upon the diaphragm, a filter disksupported within the said chamber member to prevent the passage thereinof unwanted particles, said chamber member having an entrance portbeneath the filter for connection to a conduit in which fluid pressureis subject to change for influencing the instantaneous pressure withinthe chamber so that at periods of pressure increase within the controlchamber the diaphragm supported upon the tubular member is lifted bodilyupward to provide contact between the said contact member and the twosaid contact points and whereby pressure equalization above and belowthe diaphragm member is established coincidentally with the unseating ofthe diaphragm from the tubular section and terminal points forconnecting an external circuit to the contact points so that duringperiods of actual contact thereof an electrical circuit may be broughtinto operation.

5. A detector for road vehicles including a re silient tread membermounted to be engaged by vehicles passing thereover, a longitudinalairfilled cavity forming a part of said tread member, the volume of saidcavity being variable with passage of vehicles thereover, an electricalswitching device connected with said tread member for operation inaccordance with the changes in pressure in said tread member, saidswitching device comprising a circular pipe, a circular diaphragm of adiameter slightly larger than that of said pipe arranged to bepositioned at the upper edge of said pipe, said diaphragm having adownwardly extending flange arranged to surround the upper section ofsaid pipe, a pair of contact points fixedly positioned relative to saidpipe, a contact closing member supported by said diaphragm in locationrelative to the pair of contact points such that upon movement of thediaphragm the contact points are brought electrically together, terminalpoints for connecting an electrical circuit to said contact points, andmeans provided by said diaphragm movement under changes in the volume offluid within the container for causing the said contact points to meetand for returning the contact points to their normally open state bypressure equalization within and without the chamber due to leakagebeneath the diaphragm at time periods of initiation of the contact.

6. A pneumatically-operated electric switching device comprising, incombination, a vertical tubular element, an electrically-conductingdiaphragm of a diameter slightly in excess of that of the tubularelement positioned normally to rest upon the said tubular element, saiddiaphragm being provided with a downwardlyextending flange arranged tosurround the upper portion of the vertical tubular element, a pair ofcontact points supported in fixed position relative to the tubularelement, terminal points for connecting an external electric circuit tothe pair of contact points, and a conduit connecting said tubularelement with a control chamber element so that at periods of increasesin fluid pressure within the control chamber the diaphragm is caused tomove bodily upward to engage the pair of contact points to effect anelectrical switching operation.

CECIL ROBERT WOODLAND.

REFERENCES CITED UNITED STATES PATENTS Name Date Wiley Nov. 14, 1944Number 2,362,874

